Random measurement error in visual acuity measurement in clinical settings

Abstract

ABSTRACT.Purpose: To estimate the random measurement error in visual acuity (VA) determination in the clinical environment in cataractous, pseudophakic and healthy eyes. Methods: The VAs of patients referred for cataract surgery or consultation by ophthalmic professionals were re-examined and the VA results for distance using projector acuity charts were compared. Refractive errors were also remeasured. A total of 99 eyes (41 cataractous, 36 pseudophakic and 22 healthy eyes) were examined. The healthy comparison group consisted of hospital staff. Only one eye of each person and eyes with Snellen VAs of 0.3-1.3 (logMAR 0.52 to -0.11) were included. The mean time interval between the first and second examinations was 45 days. Results: The estimated standard deviation of measurement error (SDME) of repeated VA measurements of all eyes was logMAR 0.06. Eyes with the lowest VA (0.3-0.45) had the largest variability (SDME logMAR 0.09), and eyes with VA ‡ 0.7 had the smallest (SDME logMAR 0.04). The variability may be partly explained by the line size progression in lower VAs, partly by the difference in the remeasurement of the refractive error. The difference in the average VA between examinations 1 and 2 (logMAR 0.15 versus 0.12) was considered to be of some interest because it indicates that some learning effect is possible. Conclusion: Visual acuity results in clinical settings have a certain degree of inherent variability. In this series variability ranged from SDME logMAR 0.04 (eyes with good vision) to logMAR 0.09 (in the lower vision group) in the Snellen VA range of 0.3-1.3. Changes should be judged with caution, especially in cases of decreased VA.

Results of flexible ranibizumab treatment in age-related macular degeneration and search for parameters with impact on outcome

“…4 showing permanent functional loss after deterioration in ranges that will develop in practise if a ≥5 letter difference is the indicator for re-injection. On the other hand, it seems problematic to recommend re-injections after deterioration of VA at a level of ≤5 letters, since the test--retest variability of VA measurement in patients with macular diseases has been reported to exceed 5 letters (equivalent 0.1 logMAR units) or more [19,20]. Therefore, it is desirable to find other or additional criteria (e.g., OCT data) which indicate the need for re-injections.…”

Repeatability (test‐retest variability) of refractive error measurement in clinical settings

“…A total of 81 patients referred for cataract surgery at Vaasa Central Hospital, Vaasa, Finland, or for consultation at the first author's clinic, were included. Some data on the patients were reported recently (Leinonen et al 2005). The eyes included had cataract (41 eyes), were pseudophakic (36 eyes) or healthy (four eyes).…”

“…Corneal refraction has been found to change under different blinking conditions, especially if the blinking interval increases or corneal aberrations increase as a consequence of tear film changes (Montes-Mico et al 2004). Tolerance to defocus increases when VA decreases (Legge et al 1987;Leinonen et al 2005). As a consequence, it is also likely that the accuracy of REM decreases.…”

An innovative visual acuity chart for urgent and primary care settings: validation of the Runge near vision card

“…The ETDRS chart has been shown to have relatively low test–retest variability [6, 8–12], and is likely more valid than a Snellen chart for assessing the Runge card. In contrast, Snellen charts differ by manufacturer in letters per line and progression through letter size [13], and have a relatively high test–retest variability [11, 12].…”